We just purchased a 2009 Honda Odyssey with 46,000 miles on it. The back tires are brand new, but the front ones are not great. According to Discount tire the front tires have 6/32" & 7/32" left on them. Should we go ahead and replace the front ones now so they are all the same? Or can we keep them the way they are for a while… will it effect the driving? What happens if we don’t change them now, when it’s done for them to be balanced/rotated?
Well, when you’re driving through those North Dakota blizzards, you know, you don’t want those old tires on there. 
Ok. Seriously, what kinds of conditions are we talking about? Are you in the desert with 99% dry roads and no cold to speak of? Are you in North Dakota?
What you’ll probably get here are a lot of different opinions. I buy four tires at a time, rotate them regularly, and keep up with alignment checks. So I buy four at a time and wear four at a time evenly. So I would be buying the two new ones now and putting myself on track for that.
Not everyone does it like this. Some replace two at a time. Many of those people probably don’t rotate and that is why they do two at a time. The fronts wear faster, so they get replaced first. The new ones go to the back and the ones that have been on the back go to the front.
If you keep them on there you won’t be rotating. You always keep the best tread in the rear.
We are in IL–suburbs of Chicago, so winters aren’t horrible, but this one’s been super light/dry. In the past we’ve usually bought 4 at a time, but this is the way the car came from the dealer, so aren’t sure what to do. If we don’t change them right away, any idea on how long they’ll last before they NEED to be replaced?
I would keep them until they’re down to 4/32", then put new tires on the back and move the backs to the front.
Then drive 5000 miles.
At this point front and back should still be very close in tread and you can start regular rotations.
I’d keep them until next fall, then put 2 new ones up front before next winter. The front ones will wear out faster, so I’d keep the new ones up front until they were worn down equal to the backs before rotating.
This violates the “best tires in the back” rule, but at that point all the tires will be in good condition anyway.
Chances are the original owner never rotated the tires. The fronts wear out much faster than the rears on FWD vehicles. Most tire shops will not put two new tires on the front, they move the rears to the front and put the new ones on the rear.
I would put the new tires up front and when they wear down, the rears should also be in the ballpark for replacement too, then get all four at that time.
The OP should ask himself, “if the previous owner ignored the notation about tire rotation in the Honda Maintenance Schedule…what other maintenance items might he/she have ignored?”.
While tire rotation is not as crucial an issue on a FWD vehicle as it is on an AWD vehicle, the fact remains that the vehicle’s handling will be adversely affected in extreme driving situations (rain, snow, sudden evasive manuevers) if you don’t have roughly equivalent trend on all four tires. In normal driving, you would be unlikely to notice any difference, but extreme circumstances can come about without warning, thus the potential hazard of having two worn tires and two new tires.
So–while this is not necessarily a major safety issue, I would personally worry that the previous owner was slipshod with more of the vehicle’s maintenance than just the rotation of the tires. Unless the vehicle came with full maintenance records that verify complete compliance with Honda’s maintenance schedule, the OP has to assume that NONE of the required maintenance has ever been done.
I would suggest that the OP refer to the Honda Maintenance Schedule to see what maintenance was supposed to have been done at the last major maintenance interval–which was probably 30k miles. Unless you have documentary proof that all of those procedures were done, you need to open up your wallet and have all of the listed items taken care of a.s.a.p. And, even if a transmission fluid change is not listed for 30k miles, that should be added to the list.
Some folks want the new tires on the front - most shops won’t do that.
They may not allow new tires on the front if the back ones are in really bad condition, but the back ones are brand new.
The shop I use requires them on the back, regardless. Other shops might not.
I’m not worried about other repair/maintenance issues. It was a leased car and we purchased it from the Honda dealer, it is a Honda certified used car. I think, for now, we’ll leave the tires the way they are and replace the front ones in a few months. Then see what the tire store says to do about rotating, etc.
Personally I would leave them until next winter.